1. Field of Invention
The present invention relates to road marking, and more particularly, to an apparatus and method for positioning road marking material application equipment using holographic sights.
2. Description of Related Art
Paint, thermoplastic, glass beads and other visually distinctive road marking material (hereinafter collectively referred to as “road marking material”) is often applied to roadways, runways and other paved surfaces in the form of long lines and/or intermittent stripes that define visually perceptible lanes within which vehicles and/or pedestrians can safely travel. In most instances, the road marking material is applied by one or more applicators that are transported by a vehicle that passes over the pavement surface to be marked at relatively low speed. The applicators may be mounted to a trailer that is pulled by the vehicle or, more commonly, the vehicle comprises a flat bed truck onto which the road marking material applicators are mounted.
In order to insure that the applicators are oriented in the proper and desired location above the pavement surface to be marked, it is critical that the vehicle transporting the applicators be properly positioned on the paved surface. At least four systems are known in the art for assisting vehicle operators with the proper orientation of road marking vehicles on pavement surfaces, namely: mechanical sights; optical sights; laser projection; and camera sights. Unfortunately, each of these known systems presents certain disadvantages.
Mechanical sights simply consist of a long boom or arm that extends 10–15′ away from the front of the vehicle and terminates in a tip that points downwardly toward the road surface. The boom is typically hydraulically activated. An operator of the vehicle makes steering adjustments to the vehicle in order to keep the tip of the boom pointed at a target line. Mechanical sights present at least two disadvantages. First, they extend a significant distance away from the vehicle, creating a potential traffic hazard. Second, they are not particularly accurate, and do not provide the operator with any relative reference point during use.
Optical sights are sometimes used as an alternative to mechanical sights. Optical sights employ the same basic technology as 1940's era military bomb sights. Such optical sights typically include at least one mirror, a lens and a metal reticle plate that is illuminated using an internal lighting device. An example of such an optical sight is disclosed in Brown, Jr., U.S. Pat. No. 2,974,875. Optical sights disadvantageously produce a parallax if the operator's eyes are not properly oriented with respect to the viewer. Accordingly, in order to produce accurate results, the vehicle operator must hold his or her head in the same position for extended periods of time, which causes operator fatigue and divides the operator's attention from the operation of the vehicle.
Laser projection is also sometimes used to assist operators with properly orienting vehicles transporting road marking material applicators over pavement surfaces. A laser line is projected from the vehicle to the road surface. The operator of the vehicle or equipment watches the laser mark projected on the ground, and simultaneously adjusts the position of the vehicle or equipment to maintain the laser mark on the desired target. The projected laser method is superior to mechanical and/or optical sights, at least in terms of improving operator comfort and reducing the degree to which the operator's attention is divided, but it suffers from several other disadvantages. One of the most significant disadvantages is that it is often difficult to see laser light on some types of paved surfaces, particularly in bright sunlight.
Video cameras are also sometimes used to assist operators in properly orienting road marking vehicles on pavement surfaces. A camera relays a video image to a monitor that is mounted within the cab of the vehicle. The operator of the vehicle adjusts the position of the vehicle with respect to the road until a target mark on the pavement is properly framed in the monitor. This method of aligning a vehicle on a paved surface to be marked is disadvantageous because it requires the installation of video monitors, which can be bulky in vehicle cabs, are prone to damage, and can be difficult to view in bright sunlight. Moreover, it requires that the operator of the vehicle to watch a video monitor instead of the roadway or the area around the vehicle, again disadvantageously dividing the operator's attention.